cellular immunity defense against a previously
encountered disease; primarily a function of
T cells. After a T cell recognizes a certain
antigen, it multiplies through clonal expansion
to produce several other, different T cells with
specific functions. (4.4)
census complete count of all the members of a given
population. (14.1)
central nervous system (CNS) the brain and spinal
cord. (5.1)
cerebellum the part of the brain that controls
muscle co-ordination. (5.1)
cerebral cortex the thin layer of grey matter that
covers each hemisphere of the brain, enabling the
individual to experience sensation, perform
voluntary movements, and think. (5.1)
cerebrum the largest part of the brain, in which all
the information from the senses is sorted and
interpreted, voluntary muscles are stimulated,
memories are stored, and decisions are made.
(5.1)
chain termination sequencing process used to
sequence DNA. The process relies on a modified
form of the polymerase chain reaction. (9.2)
Chargaff’s rule constant relationship in which in
any sample of DNA, the amount of adenine is
always equal to the amount of thymine, and the
amount of cytosine is always equal to the amount
of guanine. The relationship was discovered in
the late 1940s by Erwin Chargaff. (7.1)
chemical bonds the forces that hold atoms to each
other within molecules and in ionic compounds.
(1.1)
chemical energy potential energy stored in the
bonds of a molecule. (2.1)
chemical mutagen molecule that can enter the cell
nucleus and induce a permanent change in the
genetic material of the cell. (9.1)
chemiosmosis formation of ATP molecules through
the movement of hydrogen ions across an
electrochemical gradient. (3.2)
chlorophylls photosynthetic pigments within
chloroplasts that absorb light energy. (3.3)
chloroplast organelle in which photosynthesis
occurs. (3.3)
cholinesterase enzyme that breaks down the
neurotransmitter acetylcholine. The enzyme is
released from the pre-synaptic neuron, soon after
the release of acetylcholine. (5.2)
choroid layer the middle layer of the eye, which
absorbs light and prevents internal reflection. The
layer forms the iris at the front of the eye. (5.3)
chromatin fibres of material that make up
chromosomes. The fibres are composed of
about 60 percent protein, 35 percent DNA, and
5 percent RNA. (7.2)chromosome strand-like complex of nucleic acids
and protein tightly bound together. Chromosomes
contain the hereditary units, or genes. (7.1)
ciliary body thickened choroid muscle behind the
iris that controls the shape of the lens of the eye.
(5.3)
circadian rhythms daily biological cycles or regular
patterns. (6.1)
climax community self-perpetuating (secure, self-
maintaining) community with stable populations
that interact with each other and the environment
in a stable manner. In communities that are at
this stage, succession has ended. (13.1)
cloning vector a molecule that replicates foreign
DNA within a cell (e.g., a plasmid). (9.2)
closed system system that is isolated from its
surroundings. Thermal energy and atoms cannot
leave or enter the system. (2.1)
co-dominant describes a situation in which two
alleles may be expressed equally. The situation
occurs when two different alleles for a trait are
both dominant. (11.1)
codon the basic unit, or “word,” of the genetic code.
It is a set of three adjacent nucleotides in DNA or
mRNA that codes for amino acid placement on
polypeptides. (8.1)
coenzymes organic cofactors. Vitamins are a part of
many coenzymes. (2.2)
coevolution evolutionary process in which two
species of organisms that are tightly linked
(e.g., predator and prey) evolve together, each
population responding to changes in the other
population. (12.3)
cofactors inorganic ions and organic non-protein
molecules that help some enzymes function as
catalysts. (2.2)
cohort large group of individuals all born at the
same time. (14.4)
collecting duct the location where all the kidney’s
filtrate gathers to be passed to the renal pelvis.
(4.2)
colonizers the first organisms of a species to
establish themselves in a habitat. (13.1)
commensalism relationship that exists between two
or more organisms in which a symbiont benefits
from a symbiotic relationship, but the host is not
harmed. (14.3)
community all of the organisms in all the
interacting populations in a given area. (13.1)
competitive exclusion principle the theory stating
that species with niches that are exactly the
same cannot co-exist. Species with sufficiently
different niches can co-exist (possibly in limited
numbers). (14.3)572 MHR • Glossary